Thermoplastic elastomer compositions

ABSTRACT

A thermoplastic elastomer composition comprises 
     a) from 5 to 99% by weight of a block copolymer which is composed of hard blocks S made from vinyl aromatic monomers and of one or more random soft blocks B/S made from dienes and from vinyl aromatic monomers, 
     b) from 1 to 95% by weight of a plasticizer with a higher polarity than white oil and with a lower polarity than diisooctyl phthalate, 
     c) from 0 to 50% by weight of a polyolefin, and 
     d) from 0 to 60% by weight of additives, 
     where the total of a) to d) is 100% by weight. The use of the molding compositions to produce flexible or elastic moldings is described, as are the resultant moldings.

The invention relates to a thermoplastic elastomer composition,comprising

a) from 5 to 99% by weight of a block copolymer which is composed ofhard blocks S made from vinyl aromatic monomers and of one or morerandom soft blocks B/S made from dienes and from vinyl aromaticmonomers,

b) from 1 to 95% by weight of a plasticizer with a higher polarity thanwhite oil and with a lower polarity than dioctyl phthalate,

c) from 0 to 50% by weight of a polyolefin, and

d) from 0 to 60% by weight of additives,

where the total of a) to d) is 100% by weight.

The invention further relates to the use of the molding compositions forproducing flexible or elastic moldings, and also to the resultantmoldings.

Thermoplastic elastomer compositions based on hydrogenated ornonhydrogenated styrene-butadiene or styrene isoprene block copolymers(S-TPE) and, if desired, on polyolefins are known (e.g.: EP-A 0 583 228,EP-A 0 623 651, EP A 0 712 892 or EP-A 0 845 498). The physicalproperties, such as elasticity, hardness, tensile strength or adhesion,can be adjusted over a wide range via the selection of the auxiliariesand via the mixing ratios. The plasticizers used usually compriselow-aromatic paraffinic oils, naphthenic oils or oligomericpolybutadienes.

Thermoplastc elastomers or elastomer compositions based on blockcopolymers made from styrene and butadiene, with one or more random softblocks B/S, are known from WO 95/35335 and WO 96/20248. Compared withthermoplastic elastomers with a soft phase made from a pure butadieneblock, they have better processability, better weathering resistance,better thermal melt stability and better printability and paintability,e.g. with surface coatings.

The relatively high polarity of the soft blocks B/S means that theseblock copolymers have only limited compatibility with white oil, whichis usually used as plasticizer for traditional S-TPEs.

It is an object of the present invention to provide a thermoplasticelastomer composition which does not have the abovementioneddisadvantages and which, in particular when use is made of blockcopolymers with random soft blocks B/S, can be adjusted to any desiredhardness without bleed-out of the plasticizer.

We have found that this object is achieved by means of theabovementioned thermoplastic elastomer composition.

The thermoplastic elastomer composition comprises from 5 to 99% byweight, preferably from 49 to 94% by weight, of a block copolymer whichis composed of hard blocks S made from vinyl aromatic monomers and ofone or more random soft blocks B/S made from dienes and from vinylaromatic monomers.

Suitable vinyl aromatic monomers for the hard blocks S and also for therandom soft blocks B/S are styrene, α-methyl styrene, vinyl toluene ormixtures of these.

The dienes used may comprise butadiene, isoprene, piperylene,1-phenylbutadiene or mixtures of these.

Particular preference is given to block copolymers made from styrene andbutadiene.

The preparation and properties of block polymers of this type aredescribed, for example, in WO 95/35335 or WO 97/40079. They can beobtained by anionic polymerisation in a nonpolar solvent with additionof a polar cosolvent or of a potassium salt.

The morphology which results from the incompatibility of the blocks Sand B/S is important in determining the suitability of the blockcopolymers as thermoplastic elastomers. The blocks B/S aggregate in thesoft phase which forms the continuous matrix and are responsible for theelastomeric behavior at the service temperature. The blocks S arepredominantly in the form of isolated, mostly bead-shaped, inclusions,which act as physical crosslinking points.

Symmetrical three-block copolymers and star-block copolymers with outerblocks S and with one or more blocks B/S lying therebetween areparticularly suitable as thermoplastic elastomers.

The block copolymer preferably has a diene content of less than 50% byweight, preferably from 15 to 50% by weight, particularly preferablyfrom 25 to 40% by weight, based on the entire block copolymer.

The proportion of the soft phase formed from the blocks B/S is generallyat least 60% by weight, preferably from 60 to 80% by weight,particularly preferably from 65 to 75% by weight, based on the entireblock copolymer. The blocks S formed from the vinyl aromatic monomersform the hard phase, the proportion of which is not more than 40% byweight, preferably from 20 to 40% by weight, particularly preferablyfrom 25 to 35% by weight.

The random structure of the soft blocks B/S means that the glasstransition temperature is generally from −50 to +25° C., preferably from−50 to +5° C., particularly preferably from −50 to −15° C. The glasstransition temperature of the hard block S is preferably above 25° C.,particularly preferably above 50° C.

The soft block B/S is preferably composed of from 30 to 75% by weight,particularly preferably from 30 to 65% by weight, of vinyl aromaticmonomer, and from 25 to 70% by weight of diene, particularly preferablyfrom 35 to 70% by weight. The soft block B/S may have been subdividedinto two or more random soft blocks with different molecular weights ordifferent monomer compositions.

The molar masses of soft block B/S is usually from 2,000 to 250,000,preferably from 20,000 to 150,000, particularly preferably from 60,000to 120,000 [g/mol].

The molar mass of a block S is generally from 1,000 to 200,000,preferably from 5,000 to 50,000, particularly preferably from 15,000 to25,000 [g/mol]. The block copolymer may be composed of blocks S withidentical or different molar masses.

The block copolymers are usually mixed with stabilisers. Examples ofsuitable stabilizers are stearically hindered phenols such as Irganox®1076 or Irganox® 3052 from Ciba-Geigy, Basle or α-tocopherol (VitaminE).

The thermoplastic elastomer composition also comprises from 1 to 95% byweight, preferably from 4 to 49% by weight, of a plasticizer with ahigher polarity than white oil and with a lower polarity thandiisooctylphthalate. Particular preference is given to the use ofplasticizers which are only slightly more polar than white oil. Examplesof suitable plasticizers are substances which have polar groups, such asester, amide, ether, and also an aliphatic radical having 12 to 18carbon atoms. Examples of these are naturally occurring or syntheticesters of fatty acids, amides of fatty acids or esters of fattyalcohols. Preferred esters of fatty alcohols are those of citric acid,adipic acid or other di- or oligocarboxylic acids. The plasticizersmentioned may be used individually or in mixtures. It is also possibleto use mixtures with paraffinic or naphthenic oils. The best mechanicalproperties are obtained by using a mixture of a plasticizers with whiteoil, where the amount of white oil used is just that required to avoidany separation out from the block copolymer.

Reference is given to the use of plasticizers comprising vegetable oils,such as sunflower oil, or comprising a mixture of vegetable oils andwhite oil.

The hardness and flowability of the thermoplastic elastomer compositionmay be varied over a white range via the amount of the plasticizer used.

The thermoplastic elastomer composition may comprise from 0 to 50% byweight, preferably from 1 to 30% by weight, of polyolefins, such aspolyethylene, polypropylene, polybutylene, polyisobutylene,ethylene-propylene rubbers, or also EPDM rubbers. Preference is given tothe use of metallocene polyethylene with a narrow molecular weightdistribution and polyolefins with a high crystalline melting point, suchas polypropylene. Soft polyolefins may be used to improve resistance tocertain media, for example oils and solvent, and also to improve thetear propagation resistance of the elastomer composition, andcrystalline polyolefins may be used to improve heat resistance andcompression set.

Other components which may be present in the elastomer composition areadditives of any type, usually in amounts of from 0 to 60% by weight,preferably from 1 to 40% by weight, based on the elastomer composition.Examples of possible additives are fibrous or pulverulent fillers,fibrous or pulverulent reinforcing materials, stabilisers, flameretardants, pigments, dyes, and processing aids, such as lubricants andmold-release agents. Preference is given to the use of inorganicfillers, such as talc, carbonates, sulfates, oxides of varying hydrationlevels, in particular titanium dioxide, Ca silicates, Mg silicates,silicates such as Aerosil, silica gel or kieselguhr, or carbon black.Substantially transparent mixtures can be obtained by addingnanocomposites. These are phyllosilicates, such as montmorillonite,which have preferably been impregnated with hydrophobicizers, such asamines or salts with quaternized amines.

The novel molding compositions may be obtained by mixing andhomogenizing the components by the usual methods of plastics technology,and the sequence of adding the components may be varied. Examples ofsuitable mixing equipment are continuous or batch kneaders, Banburymixers, or co-rotating or counter rotating single- or twin-screwextruders.

The novel elastomer composition is elastic, can be processed as athermoplastic, and can readily be recycled by remelting. The novelelastomer composition is recommended for two-component (2C) injectionmolding, since it has excellent processability and compatibility withthermoplastics based on styrene, such as glass-clear polystyrene (GPPS),impact-modified polystyrene (HIPS), styrene-butadiene block copolymers,such as Styrolux® from BASF Aktiengesellschaft or K-Resins® (Phillips),and styreneacrylonitrile polymers (SAN) and acrylonitrile, and withbutadiene styrene polymers (ABS) polyphenylene ethers. The interfacebetween the hard component and the novel elastomer composition as softcomponent is, furthermore, transparent. Using 2C injection molding inthis way it is possible to produce flexible and rigid parts in a singlecasting. Other possible hard components are polyesters andpolycarbonate.

The novel elastomer composition may readily be painted or printed, evenwithout corona treatment. It is therefore suitable for producing elasticor flexible moldings, such as toys, parts for toys, “soft-touch”applications, such as grips or antislip surfaces, gaskets, switches,housings with sealing lips, control knobs, flexographic printing plates,shoe soles, hoses, profiles, medical items, such as infusion kits,dialysis units and breathing masks, hygiene items, such as toothbrushes,materials for insulating or sheathing cables, sound-deadening elements,folding bellows, rolls or roll coatings, and carpet backings.

EXAMPLES

A symmetrical S-B/S-S -three-block copolymer is prepared in a mannersimilar to that of the examples in WO 97/40079, except that in each case1638 g of styrene were used for the terminal blocks S and a mixture of3750 g of styrene and 3378 g of butadiene for the random soft block B/S.The polymerisation was initiated using 87.3 mmol of sec-butyllithium inthe presence of 2.36 mmol of potassium-3,7-dimethyl-3-octanoate. Theblock copolymer had a number-average molar mass M_(n), determined by GBCagainst a polystyrene standard, of 136,000 g/mol and a weight-averagemolar mass M_(W) of 163,000 g/mol.

The symmetrical S-B/S-S - three-block copolymer can absorb up to 10% byweight of white oil. The total oil content can be raised to over 50% byweight by adding sunflower oil. Table 1 gives the stability limit.

TABLE 1 Stability limit for the proportion of white oil in differenttotal proportions of oil in the thermoplastic elastomer compositionTotal oil content [% by weight] based on the elasto- mer composition  1020 30 40 50 Stability limit at proportion 100 62 42 39 32 [%] of whiteoil

The block copolymer was mixed in a ZSK 25/2 twin-screw extruder at 180°C. with a premixed white oil/sunflower oil mixture (40/60). Table 2gives the total proportion of oil and the properties of the resultantthermoplastic elastomer composition.

The DSC measurements confirm that the soft phase is plasticizedselectively by the oil mixture. The glass transition temperature of thesoft phase Tg (soft) is lowered from about −40° C. to about −80° C.,while the glass transition temperature of the hard phase Tg (hard) ispractically unaffected at about 60° C.

The Shore A hardness reduces practically linearly with rising oilcontent. Even at a Shore A hardness in the region of 10, the mechanicalproperties are still at an acceptable level. The elongation at breakreaches a maximum of 1200% at 40% by weight total oil content.

TABLE 2 Properties of the thermoplastic elastomer composition as afunction of total oil content in the form of a white oil/sunflower oilmixture (40/60). Total oil content [% by 0 5 10 20 30 40 50 weight]Glass transition temperature of soft phase Tg −38 −43 −48 −60 −65 −72−78 [° C.] Shore hardness A 82 68 63 47 30 16 11 Tear resistance [N/mm²]27 24 23 19 12 5 3 Elongation at break [%] 600 700 800 980 1150 12001100

Adding the oil can significantly improve the melt flowability MFR (Table3). It is even possible, therefore, to achieve flowabilities whichpermit injection molding at low temperatures and with short demoldingtimes.

TABLE 3 Melt flowability MFR [5 kp, 10 min⁻¹] of elastomer compositionsas a function of total oil content (white oil/sunflower oil 30/70) andof temperature Total oil content [% by weight] 0 5 10 20 30 4G 50 100°C. 2.4 9.5 30 110° C. 1.4 6.0 21.6 79 120° C. 3.3 10.0 43.0 130° C. 1.66.0 20.1 87.8 140° C. 3.7 11.6 36.3 136 150° C. 3.5 6.9 18.4 59.3 160°C. 2.9 6.3 11.3 31.5 99.6 170° C. 5.2 9.7 18.9 44.0 180° C. 9.0 16.927.8 68.7

We claim:
 1. A thermoplastic elastomer composition, comprising a) from 5to 99% by weight of a block copolymer which is composed of hard blocks Smade from vinyl aromatic monomers and of one or more random soft blocksB/S composed of from 25 to 70% by weight of dienes and 30 to 75% byweight of vinylaromatic monomers, b) from 1 to 95% by weight of aplasticizer with a higher polarity than white oil and with a lowerpolarity than diisooctyl phthalate, and which contains an ester group,amide group, or ether group, and which contains an aliphatic radicalhaving from 12 to 18 carbon atoms, or comprises a mixture of these withparaffinic or naphthenic oils, c) from 0 to 50% by weight of apolyolefin, and d) from 0 to 60% by weight of additives, where the totalof a) to d) is 100% by weight.
 2. A thermoplastic elastomer compositionas claimed in claim 1, which comprises a) from 49 to 94% by weight ofthe block copolymer, b) from 4 to 49% by weight of the plasticizer, c)from 1 to 30% by weight of the polyolefin, and d) from 1 to 40% byweight of additives.
 3. A thermoplastic elastomer composition as claimedin claim 1, in which the block copolymer comprises a symmetricalthree-block copolymer or a star-block copolymer with outer blocks S andwith one or more blocks B/S lying therebetween.
 4. A thermoplasticelastomer composition as claimed in claim 1, wherein the block copolymerhas a diene content of less than 50% by weight and has a proportion ofat least 60% by weight of the soft phase formed from the blocks B/S,based in each case on the entire block copolymer.
 5. A thermoplasticelastomer composition as claimed in claim 1, in which the plasticizercomprises an ester of a fatty acid, an amide of a fatty acid, or anester of a fatty alcohol, or mixtures of these with paraffinic ornaphthenic oils.
 6. A thermoplastic elastomer composition as claimed inclaim 1, in which the plasticizer comprises vegetable oil or a mixtureof vegetable oil and white oil.
 7. A thermoplastic elastomercompositions as claimed in claim 1, in which the polyolefin comprisespolyethylene, polypropylene, polybutylene or polyisobutylene.
 8. Aprocess for preparing elastic and flexible moldings, which comprisesusing a thermoplastic elastomer composition as claimed in claim
 1. 9. Aprocess for producing moldings with rigid and flexible regions, whichcomprises using a thermoplastic elastomer composition as claimed inclaim 1 as flexible component and an impact-modified or unmodifiedstyrene homo- or copolymer, a polyester, or polycarbonate, as rigidcomponent, in two-component injection molding.
 10. A molding with rigidand flexible regions, obtained by a process for producing moldings withrigid and flexible regions, which comprises using a thermoplasticelastomer composition comprising a) from 5 to 99% by weight of a blockcopolymer which is composed of hard blocks S made from vinyl aromaticmonomers and of one or more random soft blocks B/S composed of from 25to 70% by weight of dienes and 30 to 75% by weight of vinylaromaticmonomers, b) from 1 to 95% by weight of a plasticizer with a higherpolarity than white oil and with a lower polarity than diisooctylphthalate, and which contains an ester group, amide group, or ethergroup, and which contains an aliphatic radical having from 12 to 18carbon atoms, or comprises a mixture of these with paraffinic ornaphthenic oils, c) from 0 to 50% by weight of a polyolefin, and d) from0 to 60% by weight of additives, where the total of a) to d) is 100% byweight as flexible component and an impact-modified or unmodifiedstyrene homo- or copolymer, a polyester, or polycarbonate, as rigidcomponent, in two-component injection molding.
 11. An elastic orflexible molding, obtained by a process for preparing elastic andflexible moldings, which comprises using a thermoplastic elastomercomposition comprising a) from 5 to 99% by weight of a block copolymerwhich is composed of hard blocks S made from vinyl aromatic monomers andof one or more random soft blocks B/S composed of from 25 to 70% byweight of dienes and 30 to 75% by weight of vinylaromatic monomers, b)from 1 to 95% by weight of a plasticizer with a higher polarity thanwhite oil and with a lower polarity than diisooctyl phthalate, and whichcontains an ester group, amide group, or ether group, and which containsan aliphatic radical having from 12 to 18 carbon atoms, or comprises amixture of these with paraffinic or naphthenic oils, c) from 0 to 50% byweight of a polyolefin, and d) from 0 to 60% by weight of additives,where the total of a) to d) is 100% by weight.
 12. A toy, a part of atoy, a grip, a control knob, an antislip surfaces, a gasket, a switch, ahousing with sealing lips, a flexographic printing plate, a shoe sole, ahose, a profile, a medical item, such as an infusion kit, a breathingmask or a dialysis unit, a housing for an electrical device, a sanitaryitem, a toothbrush, an insulating or sheathing material for a cable, asound-deadening element, a folding bellows, a roll, a roller or a carpetbacking obtained from the process as claimed in claim 8.